The invention relates to a method and apparatus for the melting of sulfur and, more particularly, to a method and apparatus for the removal of moisture associated with sulfur and the melting of solid sulfur.
Elemental sulfur is produced in large quantities by recovery from underground sulfur deposits, recovery as a byproduct from treatment of sulfur-containing ores and minerals, and by production by such processes as the Claus process. Sulfur so produced may be transported to the consumer in liquid form or as a solid in various particulate forms, such as flakes, prills or granules, or slate sulfur. Sulfur obtained from some of the recovery processes and sulfur in liquid or in the various particulate forms often contain moisture, which is a hindrance in the subsequent processing of the elemental sulfur. In many instances, therefore, the elemental sulfur must be treated prior to processing for the removal of any contained moisture and for melting of the sulfur.
Typical sulfur melting and processing techniques are described in the following U.S. patents. U.S. Pat. No. 1,318,015 (Oct. 7, 1919) discloses a process for extracting sulfur from ore by heating the ore to liquefy the sulfur and subjecting the heated ore to the action of centrifugal force to separate liquid sulfur from the remainder of the ore. U.S. Pat. No. 2,019,112 (Oct. 20, 1935) teaches the fusing of solid material in a circulating flow of a melt of the same material and passing the melt in direct contact with a heating gas. U.S. Pat. No. 2,850,372 (Sept. 2, 1958) discloses a method and apparatus for continuously melting particles by propelling particles into suspension in a peripherally confined current of a gas while applying heat transversely to the said current. U.S. Pat. No. 3,355,259 (Nov. 28, 1967) relates to melting sulfur by adding sulfur to a bath of molten sulfur and supplying heat by submerged combustion of gas or addition of hot combustion product gases to the molten sulfur.
The melting of particulate solids by charging the particles into a circulating molten mass of the solids is described in U.S. Pat. No. 3,369,873 (Feb. 20, 1968). The molten mass is heated by withdrawing a portion near the surface, heating said withdrawn portion above the melting point of the solids, and returning the heated portion to the molten mass near the bottom thereof to establish a generally upward flow.
According to another conventional technique, sulfur is melted in sulfur melting pits. Solid sulfur is fed into an agitated bath of molten sulfur and the additionally required heat is supplied with steam coils immersed in the molten sulfur or external to the melting pit, or by direct heat exchange using hot combustion gases. This conventional technique has two major draw-backs, especially when moisture is present with the solid sulfur. The first drawback is the formation of large amounts of persistent foam and the second drawback is the required large amount of energy to heat and evaporate moisture relative to the heat capacity of molten sulfur. Another disadvantage is the need for intimate mixing of the solid sulfur with the molten sulfur in order to avoid localized cooling of the molten sulfur which might cause difficulties in controlling the process due to sharply increased viscosity of the cooler sulfur.
Thus, none of the prior art processes provides means for the removal of moisture associated with sulfur.